Crazy Electrical issues

[Webmorris]

Heading out on a new trip this last week and noticed after heading out that without the generator running I had no 120v at all. checked the batteries and saw 13.4 volts on batteries. After much checking and hair pulling I finally noticed the T class fuse between the house battery bank and the inverter was bad based on checking the voltage on both sides and the continuity between. That said the voltage between without the generator was 13+ volts on the battery side and 0.0 volts on the inverter side. With the generator running and much longer than expected the voltages were 13+ on the battery side and 15+ on the inverter side. The inverter itself would take quite a time to see anything other than a dead battery at 0.0 volts and click and click every 5 seconds until it would finally see a voltage to send to the battery bank at 15+ volts and then everything would work fine inside the coach. When the generator was shut off everything 120v would shut down. I replaced the T fuse with a compatible 300 amp fast blow fuse which is what I found in the coach, though after looking at the manual for the Magnum inverter model MS2012? it calls for a 400amp slow blow fuse and in talking with Magnum support they suggest trying that fuse to see if it fixes it. Mind you I've had this same system boondocking in AZ for a month in January with no troubles at all. I've also had the battery bank being 3 100amp hour lithium batteries go out completely to 0.0 volts after running the generator for quite some time but may attribute that to the BMS shutting it down? I've also had some remote 120v outlets go out unexpectedly. Makes me wonder my inverter going bad? But see no way to really test it. At a loss other than that T fuse....Crazy I know.....

[Archer2]

I’m not sure that I am following what you are describing but what I think you are saying is that 1. You discovered that the DC fuse between the batteries and the inverter/Charger was open. OK, well that’s not good and needs to be corrected. 2. Without the generator running you measured 13V on the battery side of the blown fuse and 0V on the I/C side. That’s exactly what you should see. Without AC from generator or shore power the Charger will not work, hence 0V. 3. You fired up the generator and the Charger came on and you still measured 13V on the battery side of the blown fuse and 15V (from the charger) on the charger side. However, the Charger can’t charge the batteries because there is no current, (because the fuse is open). 4. When you turn the generator on the 120VAC stuff comes on but when the generator is off the 120VAC goes away. Yes, the generator AC is being passed thru the inverter and powers the various stuff on the inverted output but when you turn the generator off then the 120VAC goes away because with no connection to the batteries (the fuse is open) the inverter cannot make 120VAC.
My recommendation would be first, replace the fuse with the correct value replacement. Second, then connect to shore power or run the generator so the inverter/Charger can charge the batteries.

[Persistent]

Do what the Magnum help person said. Replace the fuse. Buy two. If it blows again, you have to fix something else and will need another fuse.